JPH066759A - Non-linear emphasis circuit - Google Patents

Abstract

PURPOSE:To eliminate the deterioration in picture quality in a non-linear empha sis circuit. CONSTITUTION:The non-linear emphasis circuit is provided with a mutual conductance circuit 4 for inputting in-phase a signal from an input terminal 1, limiter amplifier 3 for inputting the signal from the input terminal 1, a capacitor 5 connected between the output of the amplifier 3 and the output of the circuit 4, and a buffer circuit 6 for inputting a node between the circuit 4 and the capacitor 5 and connecting its output to an output terminal and the output of the circuit 6 is connected to the reverse phase input terminal of the circuit 4. Consequently picture quality deterioration due to the waveform distortion of a high band fine signal due to phase shift can be eliminated and reproducibility in a high band can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-linear emphasis circuit, and more particularly to a video tape recorder (VTR).
The present invention relates to a non-linear emphasis circuit in video signal processing.

[0002]

2. Description of the Related Art Generally, in the recording / reproducing by the FM system which is carried out by a VTR, there is a characteristic that when FM demodulation, the noise increases as it goes to a higher frequency range called so-called triangular noise, and the SN ratio of a minute signal of a video signal is improved. In order to do so, the non-linear emphasis circuit emphasizes the high range of the minute signal of the video signal during recording, and attenuates the high range of the minute signal during reproduction to suppress noise.

Next, an example of a conventional non-linear emphasis circuit is shown in FIG. In FIG. 4, in this conventional example, a high-pass filter (HPF) 7, a limiter amplifier 8 for inputting an input signal Vin input from the input terminal 1 via the high-pass filter 7, and an input signal input from the input terminal 1 are shown. The adder circuit 9 adds the output signals of the limiter amplifier 8 from Vin and outputs the signal Vo to the output terminal 2 of the linear emphasis circuit.

When the input signal Vin is a very small signal, the limiter amplifier 8 is not limited. Therefore, the output of the HPF 7 is amplified by the limiter amplifier 8 and the adder circuit 9 is added to the input signal Vin to emphasize the high frequency range. .

When the input signal Vin has a large amplitude, the limiter amplifier 8 limits the input signal Vin, so that the amount of emphasis in the high frequency band becomes small. The frequency characteristics of the amplitude H of these input signals Vin and the output of non-linear emphasis are as shown in FIG.

In FIG. 3, the horizontal axis represents frequency and the vertical axis represents response, and when the amplitude H of the input signal Vin is large,
The characteristic curve becomes, and as the amplitude H of the input signal Vin becomes smaller, the characteristic curve becomes, and so on.

In addition, at the time of reproduction, if the output of the limiter amplifier 8 has a phase opposite to that at the time of recording to be an inverted output, the high frequency band can be attenuated.

[0008]

In the conventional non-linear emphasis circuit described above, the high frequency minute signal extracted by the high pass filter 7 and the limiter circuit 8 is added to the adder circuit 9.
Since it is added to the input signal Vin to emphasize the high frequency band, the higher the cut-off frequency of the high-pass filter 7, the larger the phase around the high-pass filter 7, and the deviation from the input signal Vin as shown in FIG. By the way, the high frequency minute signal is added, and there is a problem that the waveform (c) of the high frequency minute signal of the output signal Vo is distorted and the image quality is deteriorated. That is, the waveform (a) of the input signal Vin of FIG. 6 and the output signal waveform (b) of the limiter amplifier 8 are added by the adder circuit 9 to obtain the distorted waveform (c) of the output signal Vo.

In the normal state of the conventional non-linear emphasis circuit, the waveform (a) of the input signal Vin and the waveform (b) of the output signal of the limiter amplifier 3 are as shown in FIG.
There is no phase shift, and the waveform (c) of the output signal Vo has no distortion.

An object of the present invention is to solve the above problems and to provide a non-linear emphasis circuit which can obtain an output signal with less distortion.

[0011]

The non-linear emphasis circuit of the present invention comprises a transconductance circuit for inputting an input signal at an input terminal as an in-phase input, a limiter amplifier for receiving an input signal at the input terminal, and the limiter. A capacitor whose both ends are connected to the output of the amplifier and the output of the transconductance circuit, and a signal obtained by adding the output signal of the limiter amplifier to the output signal of the transconductance circuit via the capacitor, and an output terminal And a buffer circuit for outputting an output signal, and the output of the buffer circuit is fed back to the negative phase input terminal of the transconductance circuit.

[0012]

1 is a block diagram showing a non-linear emphasis circuit according to an embodiment of the present invention. 1, in the present embodiment, an input signal Vin of an input terminal 1 is used as an in-phase input, a transconductance (gm) circuit 4 having a high impedance and a current output, and a limiter amplifier 3 having an input signal Vin of the input terminal 1 as an input. And a capacitor (C) 5 connected between the output of the limiter amplifier 3 and the output of the transconductance circuit 4, and the connection point between the output of the transconductance circuit 4 and the capacitor 5 as input, and its output as an output terminal. 2 is connected to the buffer circuit 6 and the output signal Vo of the buffer circuit 6 is connected to the anti-phase input terminal of the transconductance circuit 4.

Next, regarding the operation of the embodiment shown in FIG. 1, when the amplitude of the input signal Vin of the input terminal 1 is a minute input signal smaller than the limiter level of the limiter amplifier 3 and when the large amplitude input signal is larger than the limiter level. I will explain separately.

(1) At a minute signal In this case, if the gain of the limiter amplifier 3 is Av times, the output of the limiter amplifier 3 becomes Av times the input signal (denoted as Vin), so that the transfer function T of FIG. (S) is
The following expression (1) is obtained.

[0015]

When the frequency is sufficiently lower than 1 / 2πCr, the gain becomes [1] and the input signal Vin becomes the output signal Vo as it is, and when the frequency is sufficiently higher than 1 / 2πCr, the output is Av times the input signal Vin. The signal becomes a signal and is emphasized in the high frequency range, and the frequency characteristic when the amplitude in the low frequency band is used as a reference is as shown in the waveform of FIG.

(2) When a large-amplitude signal is input In FIG. 2, a characteristic diagram of the limiter amplifier 3 is shown. The horizontal axis is the limiter amplifier input I and the vertical axis is the limiter amplifier output O, and the limiter level width is shown. The limiter operates at W or more.

In this case, since the input / output characteristic of the limiter amplifier 3 is as shown in FIG. 2, the input signal Vin above the limiter level is output at a constant level, and Av of the transfer function equation (1) becomes non-linear (non-linear), As for the frequency characteristic, as in the waveform of FIG. 3, the amount of emphasis in the high frequency band is small, and the characteristic of non-linear emphasis is obtained.

Further, as explained at the beginning of the prior art,
It is necessary to restore the frequency characteristics of the signal to the original through a circuit that emphasizes the high frequency band during recording and attenuates the high frequency band that is the reverse characteristic during recording, but it is easy to set the polarity of the limiter amplifier 3 in FIG. The characteristic opposite to that of high-frequency emphasis is obtained.

[0020]

As described above, according to the present invention, when the input signal is equal to or lower than the limiter level of the limiter amplifier, the characteristics of the high-pass filter are obtained, and the high frequency component is added to the input signal as in the conventional example of FIG. Since this is not a configuration, there is an effect that the image quality is not deteriorated due to the waveform distortion of the high frequency minute signal due to the phase shift, and the high frequency reproducibility is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a non-linear emphasis circuit according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing the input / output characteristics of the limiter amplifier of the embodiment shown in FIG.

FIG. 3 is a characteristic diagram showing frequency characteristics of non-linear emphasis.

FIG. 4 is a block diagram showing a conventional nonlinear emphasis circuit.

FIG. 5 is a timing diagram showing operation waveforms of a conventional non-linear emphasis circuit in a normal state.

FIG. 6 is a timing chart showing operation waveforms showing a problem of the conventional non-linear emphasis circuit.

[Explanation of symbols]

 1 Input Terminal 2 Output Terminal 3,8 Limiter Amplifier 4 Mutual Conductance Circuit 5 Capacitor 6 Buffer Circuit 7 High Pass Filter (HPF) 9 Adder Circuit H Input Signal Amplitude I Limiter Amplifier Input O Limiter Amplifier Output Vin Input Signal Vo Output Signal W Limiter Level (A), (b), (c) Waveform

Claims (2)

[Claims] 1. A transconductance circuit having an input signal of an input terminal as an in-phase input, a limiter amplifier having an input signal of the input terminal as an input, and both ends of an output of the limiter amplifier and an output of the transconductance circuit. A buffer circuit that receives a signal obtained by adding an output signal of the limiter amplifier to an output signal of the transconductance circuit via the capacitor and outputs an output signal to an output terminal, A non-linear emphasis circuit characterized in that the output of the circuit is fed back to the anti-phase input terminal of the transconductance circuit. 2. The nonlinear emphasis circuit according to claim 1, wherein the output polarity of the limiter amplifier is inverted and input to the capacitor.